1. Field of the Invention
The present invention relates to positioning control for stopping a control object at a control target position, and more particularly to a positioning apparatus for driving the control object to the target position by rotation speed control and braking operation.
2. Prior Art
The present applicant has disclosed, in Japanese Unexamined Patent Publication No. 4-43412, an intermittent rotation driving control system comprising an intermittent rotation driving control mechanism and a clutch controller thereof, the intermittent rotation driving control mechanism including an input shaft coupled to a rotation driving source through a main clutch mechanism, two gear mechanisms coupled to the input shaft through a control clutch, and an output shaft coupled to the gear mechanisms which are engaged opposite to each other.
The intermittent rotation driving control system operates in the following manner. After the output shaft reaches a preset first decelerating position during rotation of the output shaft performed by selectively turning on the main clutch mechanism and either of first and second control clutch mechanisms, the first and second control clutch mechanisms are turned on at the same time to perform braking operation. Every time a speed has a value equal to or less than a predetermined value, the braking operation is released. After the output shaft reaches a second decelerating position, the first and second control clutch mechanisms are alternately turned on and off in order to compensate for a displacement of the output shaft from a target position. Thus, a control object is stopped at the target position.
The clutch controller forming such a system comprises a rotation speed detector for detecting a rotation speed of the output shaft, rotation speed discriminating means having a speed level discriminating circuit for discriminating a level of a speed signal output from the rotation speed detector and for outputting a brake release signal when the speed signal is reduced to a predetermined level, pulse generating means for generating a pulse signal with the rotation of the output shaft, rotation angle detecting means including a counter circuit section for counting the pulse signal sent from the pulse generating means, a direction discriminating circuit for discriminating a rotation direction of the output shaft, a displacement discriminating circuit for discriminating a displacement area which fluctuates around the control target position of the output shaft, and a control circuit for turning on and off a clutch in response to a normal-reverse rotation command signal, first and second decelerating position reach signals and a direction discriminating signal sent from the rotation speed discriminating circuit.
According to such a system, the intermittent rotation driving mechanism for giving a high torque output can be driven instantaneously and intermittently with high precision. Therefore, it is possible to perform positioning control having a high output torque which cannot be performed in the prior art. Furthermore, even if a load having great inertia force is applied, intermittent rotation driving operation can be performed with high precision.
Conventionally, there have been a positioning apparatus for performing positioning operation only by braking using a brake device and a positioning apparatus for braking a control object by using only an electronic brake, for example, DC dynamic braking of an inverter controller, thus performing the positioning control.
However, the intermittent rotation driving control system has the following problems.
More specifically, the first and second clutch mechanisms are turned on at the same time so that the rotation speed of the output shaft is decreased during deceleration braking operation. During damping oscillation, the first and second clutch mechanisms are alternately turned on and off so that the output shaft repeatedly performs reverse rotation to oscillate. In other words, a slide of the clutch mechanism is utilized to perform speed control. Therefore, it is necessary to allow for a rise in a temperature caused by heat generation of the clutch mechanism.
In addition, the intermittent rotation driving mechanism for performing the intermittent rotation driving operation is required. Consequently, a size of the apparatus and a cost thereof are increased. Furthermore, such a system cannot be exactly applied to an existing positioning control system for performing inverter control and additionally needs a mechanism portion.
In consideration of the foregoing, it is an object of the present invention to provide a positioning apparatus capable of performing positioning control with high precision without using the intermittent rotation driving control mechanism.